Digital inkjet printing is widely used in imaging graphics, banners, labels, etc. This printing technology attracts a wide range of applications due to its short turnaround time, and flexible modification of the image used for each impression.
Based on the properties of the printing ink, a majority of inkjet printing technologies can be classified as solvent based inkjet, water based inkjet, UV inkjet, and latex inkjet. For UV inkjet printing, a UV inkjet printer must be used which emits a UV beam to solidify the printed ink. Latex inkjet printers are equipped with one or more high capacity heater(s) to evaporate water in the printed ink in a relatively short time. Solvent inkjet printers, especially those using high boiling point solvent in the ink, and water inkjet printers typically do not have enough heating capacity to remove the residual liquid in the printed ink. Instead, those printers require print media able to absorb most of the liquid ejected from the print head in a relatively short time to control the formation of ink dots on the media and attain a “dry to touch” characteristic after printing. For example, Eco-Sol Max ink used in Roland Eco-Sol inkjet printers contains over 90% of a mixture of diethylene glycol diethyl ether (boiling point=189° C.), r-butyrolactone (boiling point=204° C.), and tetraethylene glycol dimethyl ether (boiling point=275° C.). The printer heating bed is typically heated up to 50° C. Dye or pigment water based inkjet ink used in desktop or narrow web printers typically contains 90% water and the printers equipped with these inks generally have no media heating capability.
Most ink receptive layers used in currently available print media designed for solvent inkjet printers use solvent swellable polymers and absorptive filler to “lock in” the liquid in the media during print. The selection of the polymers is based on solubility parameters between polymer and solvent. The solubility parameter between polymer and solvent should be such that the polymer can swell with solvent. Typical polymers used in conventional ink receptive layers include vinyl, acrylics, polyacrylate, polyurethane, amorphous polyester, polyether, polyvinyl alcohol, etc. In order to provide enough absorption capacity, the ink receptive layer has to be thick enough, typically at least 25 microns, to absorb the volume of liquid ink deposited on the print media. This makes the resulting media material relatively costly.
Polyolefins are much less expensive than the swellable polymeric materials previously noted. The average cost of polyethylene and polypropylene is approximately 25% of the cost of polymers such as polyurethane, polyvinyl alcohol, amorphous polyester, etc. However, solid polyolefin films such as polyethylene and polypropylene have no affinity to most polar solvents used in solvent inkjet printing and water used in water inkjet printing in the market. As result, films with a layer or coating of polyolefin(s) as an ink receptive surface do not sufficiently absorb the ink liquid and thus the media is relatively wet after print and exhibits poor printing image quality, namely low image resolution and ink bleeding. As will be appreciated, this is undesirable.
Accordingly, a need remains for strategies by which polyolefin films and other materials which do not have a sufficient affinity for polar solvents used in solvent inkjet printing and/or water used in water inkjet printing, can be used as print media. A need also exists for a new class of print media which addresses the above noted problems.